Position-measuring device

Abstract

A position-measuring device includes a scale and a scanning unit movable relative to the scale in a measurement direction. The scale has an incremental measuring graduation and reference marks spaced apart from each other. The scale has a first marking track containing a first marking associated a reference mark and a second marking spaced apart from the first marking. The scanning unit has a first and a second detector spaced apart from each other. A distance between the detectors is greater than a length of the first marking and less than a length of the second marking. The scanning unit is configured to produce a reference pulse based on only the first detector of the two detectors generating a scanning signal, and to produce a switching signal when both the first detector and the second detector generate a scanning signal.

What is claimed is: 
     
       1. A position-measuring device, comprising:
 a scale having an incremental measuring graduation and a plurality of reference marks spaced apart from each other in a measurement direction, a reference mark pulse being generatable by scanning one of the reference marks, the scale having a first marking track containing a first marking associated with one of the reference marks and a second marking spaced apart from the first marking in the measurement direction, the second marking being longer than the first marking in the measurement direction, a switching signal being generatable by scanning the second marking; and 
 a scanning unit movable relative to the scale in the measurement direction, the scanning unit having, for purposes of scanning the first marking track, a first detector and a second detector spaced apart from the first detector in the measurement direction, a distance between the first detector and the second detector being greater than a length of the first marking and less than a length of the second marking, each of the detectors being configured to generate a scanning signal in response to scanning one of the markings, the scanning unit being configured to produce the reference pulse based on only the first detector of the two detectors generating a scanning signal, and to produce the switching signal when both the first detector and the second detector generate a scanning signal. 
 
     
     
       2. The position-measuring device as recited in  claim 1 , wherein the first detector is located on a side of the two detectors on which the first marking is located with respect to the second marking. 
     
     
       3. The position-measuring device as recited in  claim 1 , further comprising a reference mark detector for generating reference mark signals, the reference mark detector being disposed in the scanning unit and being configured to scan the plurality of reference marks, the plurality of reference marks being located in the first marking track. 
     
     
       4. The position-measuring device as recited in  claim 3 , wherein the reference mark detector is located a first distance from the first detector in the measurement direction, and the first marking is located the first distance from the associated reference mark. 
     
     
       5. The position-measuring device as recited in  claim 4 , wherein the second detector is located a second distance from the first detector in the measurement direction, the second distance being different from the first distance. 
     
     
       6. The position-measuring device as recited in  claim 1 , wherein the second marking is located at a limit position of the scale, the limit position of the scale being indicated by the switching signal. 
     
     
       7. The position-measuring device as recited in  claim 1 , wherein the scale has a further marking track containing a further marking, and the scanning unit includes a further detector configured to scan the further marking. 
     
     
       8. The position-measuring device as recited in  claim 7 , wherein the scanning unit is configured to produce a further switching signal when the further detector scans the further marking. 
     
     
       9. The position-measuring device as recited in  claim 1 , wherein the detectors are light-sensitive detectors, the first marking track is reflective, and the markings are light-absorbing. 
     
     
       10. The position-measuring device as recited in  claim 9 , wherein the light-absorbing markings are strips that are adhesively bonded to the scale.